The present invention relates to a method of manufacturing a magneto-resistance element, and in particular, to a method of manufacturing a magneto-resistance element having a large rate of change of magneto-resistance (MR). The magneto-resistance element made by the method of the present invention is suitably applied to a head for reproducing a magnetic signal written into a hard disk, floppy disk, magnetic tape, or the like.
Conventionally, as structure of a magneto-resistance, are widely known an artificial lattice type (A) of a structure in which ferromagnetic layers are laminated a plurality of times on a surface of a substrate body putting non-magnetic layers (spacers) between them, and a spin valve type (B) of a structure in which ferromagnetic layers are laminated on a surface of a substrate body putting non-magnetic layers between them and an antiferromagnetic layer is formed on the surface of said ferromagnetic layer provided last.
To manufacture the magneto-resistance element of such a structure, since each layer is an ultra thin film having thickness of several nm, technological development has been demanded for sequentially laminating high purity thin films superior in flatness, under an atmosphere as clean as possible. Japanese Patent Application No. 7-193882 is mentioned as an example of such technique. The specification of that patent application describes that by making oxygen concentration in the above described structure less than or equal to 100 wt ppm, a magneto-resistance element having a high MR ratio is obtained. Further, it reports that such structure having a trace of oxygen concentration is superior in flatness.
However, in the present state that higher recording density is being promoted, it is strongly desired to realize a magneto-resistance element that can reproduce a magnetic signal with higher sensitivity, i.e., a magneto-resistance element having a higher MR ratio (at room temperature) as compared to the conventional one. To accomplish it, it is desired to develop a manufacturing method that is superior in controllability and can easily form a magneto-resistance element that is better in its flatness of its lamination interfaces and has fewer defects in its crystal structure.
An object of the present invention is to provide a method of manufacturing a magneto-resistance element having such a high MR ratio that a magnetic signal can be reproduced with higher sensitivity.
The present invention provides a method of manufacturing a magneto-resistance element of a structure in which ferromagnetic layers are laminated a plurality of times on a surface of a substrate body putting non-magnetic layers therebetween, comprising steps of:
depressurizing an inside of a deposition chamber in which said non-magnetic layers and said ferromagnetic layers are formed, to an ultimate degree of vacuum at a level of 10xe2x88x929 Torr or less;
introducing a gas a containing at least oxygen or water into said deposition chamber to change the ultimate degree of vacuum inside the deposition chamber to a certain pressure higher than the level of 10xe2x88x929 Torr, then, introducing a gas b consisting of Ar, and carrying out plasma etching processing of the surface of said substrate body using a mixed gas of said gas a and said gas b; and
sputtering prescribed targets in said deposition chamber using the mixed gas of said gas a and said gas b to form said non-magnetic layers and said ferromagnetic layers by a sputtering technique on the substrate body processed by said plasma processing.
In the method of manufacturing a magneto-resistance element according to the present invention, first, owing to the step of depressurizing the inside of the deposition chamber in which said non-magnetic layers and said ferromagnetic layers re formed to an ultimate degree of vacuum at a level of 10xe2x88x929 Torr or less, it is possible to remove substances absorbed discontinuously onto the substrate body at atmospheric pressure, from the surface of the substrate body in the stage preceding the film formation.
Next, owing to the step of introducing the gas a containing at least oxygen or water into the deposition chamber to change the ultimate degree of vacuum inside the deposition chamber to the certain pressure higher than the level of 10xe2x88x929 Torr, then, introducing the gas b consisting of Ar, and carrying out plasma etching processing of the surface of the substrate body using the mixed gas of said gas a and said gas b, it is possible to make a controlled amount of impurities such as oxygen be uniformly absorbed onto the surface of the substrate body from which impurities have been sufficiently removed in the step of degreasing the ultimate degree of vacuum to the level of 10xe2x88x929 Torr or less.
Then, owing to the step of sputtering the prescribed targets in said deposition chamber using the mixed gas of said gas a and said gas b, to form said non-magnetic layers and said ferromagnetic layers by a sputtering technique on the substrate body processed by said plasma processing, it is possible to form a multi-layer film under an atmosphere that is controlled in its cleanliness although that cleanliness is low. By this, there are many impurities on the surface of the substrate body and on the surfaces of the films and it becomes difficult for crystals to grow, and accordingly, diameters of crystal grains become smaller. Accordingly, at the same time, the flatness of the lamination interfaces is improved. Or, the impurities act like a surface active agent to suppress aggregation of atoms constituting the non-magnetic layers and the ferromagnetic layers so that the interfaces are flattened. As a result, a magneto-resistance element having a high MR ratio is obtained.
Further, in the method of manufacturing a magneto-resistance element according to the present invention, by making the ultimate degree of vacuum inside the deposition chamber more than or equal to 3xc3x9710xe2x88x927 Torr and less than or equal 8xc3x9710xe2x88x925 Torr, after introducing said gas a, in said step of carrying out the plasma etching processing and said step of film formation by a sputtering technique, there is obtained a magneto-resistance element having a higher MR ratio than a magneto-resistance element obtained by depressurizing the inside of the deposition chamber to an ultimate degree of vacuum at a level of 10xe2x88x929 Torr or less, etching the surface of the substrate body using only Ar gas, and then forming the non-magnetic layers and the ferromagnetic layers by a sputtering technique.
Further, when the ultimate degree of vacuum inside the deposition chamber is more than or equal to 3xc3x97xe2x88x926 Torr and less than or equal to 2xc3x9710xe2x88x925 Torr, after introducing said gas a, in said step of carrying out the plasma etching processing and said step of film formation by a sputtering technique, there is obtained a magneto-resistance element having an MR ratio twice as high as the magneto-resistance element obtained by depressurizing the inside of the deposition chamber to the ultimate degree of vacuum at the level of 10xe2x88x929 Torr or less, etching the surface of the substrate body using only Ar gas, and then forming the non-magnetic layers and the ferromagnetic layers by a sputtering technique.
As a film-formation apparatus suitable for carrying out the method of manufacturing a magneto-resistance element according to the present invention, is mentioned a facing target DC sputtering system (made by Osaka Vacuum, Ltd.) shown in FIGS. 5 and 6, for example. FIG. 5 is a system diagram showing a vacuum pumping system of the apparatus, and FIG. 6 is a schematic cross section of the inside of a sputtering chamber of the apparatus shown in FIG. 5, seen from above. In FIG. 5, reference numeral 501 refers to a load-lock chamber, 502 to the sputtering chamber, 503 to a gate valve, 504 to a means for moving a substrate body, 505 to a turbo-molecular pump, 506 to a scroll vacuum pump, 507 to an auxiliary valve, 508 to a leak valve, 509a to a variable leak valve, 510 to a high purity N2 gas supply line, 511 to a composite molecular pump, 512 to a molecular drag pump, 513 to a scroll vacuum pump, 514 to an ion gauge, 515 to a Pirani gauge, 516 to an auxiliary valve, 517 and 518 to leak valves, 519 to a variable leak valve, and 520 and 521 to high purity Ar gas supply lines.
In FIG. 6, a reference numeral 601 refers to a substrate body, 602 to a substrate body holder, 603 to a Co deposition chamber, 604 to a Cu deposition chamber, 605a and 605b to shutters, 606a and 606b to anti-adhesion plates, 607 to a Co target, 608 to a magnet, 609 to a Cu target, 610 to a magnet, 611 to an AC power supply, 612 and 613 to DC power supplies, and 614 and 615 to cathodes.
In the facing target sputtering system such as shown in FIGS. 5 and 6, two planar targets of the same size are arranged to face each other, and permanent magnets are arranged within a cathode so that a plasma focusing magnetic field is applied perpendicularly to a target. Both targets functions as reflecting electrodes for a high speed xcex3 electron (secondary electron) emitted from a target and accelerated in a cathode fall, and thereby, this secondary electron is confined between both targets and secondary electron impact on the substrate body arranged outside the area between the targets is suppressed. Further, while the secondary electrons are reciprocating within a space, they raise energy of electrons within the plasma, or, by colliding with the atmospheric gas, they promote ionization of the gas and develop high density plasma. Owing to thus-described characteristics, it is advantageous in that a rise in substrate temperature during film formation can be reduced, and film formation can be carried out under lower gas pressure as compared to an ordinary planar magnetron sputtering system.
In the apparatus of FIG. 5, the inner wall of the sputtering chamber 502, in which film formation is carried out, is subjected to electro polishing and chromium oxidation passivation (CRP) treatment to reduce gas emitted from the inner wall. The sputtering chamber 502 is provided with the load-lock chamber 501 via the all-metal gate valve 503. By this, the sputtering chamber 502 is not opened to the atmosphere at the time of setting the substrate body, so that the degree of vacuum can be maintained.
When a pump utilizing oil is employed in the vacuum pumping system, it is conjectured that cleanliness of the atmosphere and the surface of the substrate body is reduced owing to oil diffusion toward the load-lock chamber 501 and the sputtering chamber 502. Accordingly, all the pumps employed were oil-free pumps. To carry out vacuum pumping, a magnetic bearing type composite molecular pump (TG700M, made by Osaka Vacuum, Ltd.) 511, a molecular drag pump (made by Alcatel, Ltd.) 512, and a scroll vacuum pump (ISP-500, made by Iwata Air Compressor Mfg. Co., Ltd.) 513 were employed for the sputtering chamber 502.
And, for the load-lock chamber 501, were employed a magnetic bearing type turbo-molecular pump (ET300 made by Ebara Corp.) 505 and a scroll vacuum pump (ISP-500, made by Iwata Air Compressor Mfg. Co., Ltd) 506. As the sputtering gas, Ar gas having the impurity concentration of the order of ppt was used and introduced into the sputtering chamber 502 using an SUS pipe 521 processed by CRP treating. Impurity concentration at the use point was about 1 ppb. To control the Ar gas, were employed an automatic pressure regulator (not shown) and a mass flow controller (not shown), processed by CRP treatment at gas contact portions in their inner surfaces. Degree of vacuum of the sputtering chamber 502 was measured by a wide range ionization gauge (MIG-430, made by Anelva Co., Ltd.) 514 and a Pirani gauge (TM20, mady by Leybold Co., Ltd.) 515. Degree of vacuum of the load-lock chamber 501 was measured by a wide range ionization gauge (not shown).
FIG. 6 is a schematic cross section of the inside of the sputtering chamber 50 of FIG. 5, seen from above. By rotating the substrate body holder 602 located in the center of the sputtering chamber, it is possible to form a multi-layer film on the substrate body 601. The distance between the targets was set at 100 mm, and the distance between the center of the targets and the substrate body was set at 90 mm. Further, since the plasma focus magnetic field is applied perpendicularly to a target, there is a leakage field of about 30 Oe in the plane of the substrate body at the position of the surface of the substrate body. The permanent magnets 608 or 610 are arranged in order that the leakage field at the position of the surface of the substrate body is in the same direction even when the substrate body 601 is rotated at the time of film formation. Rotation of the substrate body holder 602 and opening and closing of the shutter 605a or 605b are controlled by stepping motors (not shown) via rotating feed-throughs (not shown).